1. Field of Invention
The present invention is directed to electrochemical systems and in particular to solution phase catholyte electrochemical systems.
2. Description of the Prior Art
In the present art, electrochemical systems produce useful electric currents as a result of chemical reactions conducted between an anode and a cathode. For example, these reactions are created by passing a liquid electrolyte, between the anode and the cathode. A typical electrolyte is an aqueous saltwater solution, such as seawater. Power sources or primary batteries based on electrochemical systems employing aqueous saltwater electrolytes have been developed. These power sources use aluminum and magnesium anodes, which are preferred for their high faradaic capacity, low atomic weight and high standard potentials.
Since seawater is a readily available source to be used as an aqueous electrolyte, electrochemical batteries are particularly useful for naval vessels. Other applications include providing power for sonobuoys.
In general, electrochemical energy sources have been developed to permit high voltages, to have large storage capacities, to operate safely and to deliver the stored energy reliably over extended discharge times. One type of electrochemical energy source is a high energy density aluminum-aqueous primary battery or semi-fuel cells (SFC) suitable for high current density (>500 mA/cm2) applications, that is current densities greater than 500 mA/cm2.
Examples of these electrochemical batteries include the aluminum-silver oxide (Al—AgO) battery and the aluminum-hydrogen peroxide (Al—H2O2) SFC. These two couples have produced current at the high rates of 500-1600 mA/cm2 with resultant specific energy densities of 190 Wh/kg for the Al—AgO battery and 210 Wh/kg for the Al—H2O2 SFC.
Other seawater batteries have been developed, all of which include solid cathodes, including silver chloride, cuprous chloride, lead chloride, cuprous iodide, cuprous thiocyanate and manganese dioxide.
In some applications, the seawater electrolyte is forced or drawn between an anode and a cathode that are electrically coupled through a load. Methods that have been used to force or draw the electrolyte through the electrochemical cell include using thermal and density differences or using active pumping. The voltage that is produced by these electrochemical batteries is controlled, for example, by using conventional voltage regulators. Voltage regulators are disadvantageous, however, in that they generally consume a relatively high level of power and are not highly reliable.
It is also known in the art that the output voltage of an electrochemical battery is proportional to the rate of flow of electrolyte through the cell containing the anode and cathode due to the change in operating temperature of the battery associated with variations in the flow rate of the electrolyte. Therefore, in other applications, control of the output voltage can be achieved by controlling the temperature of the electrochemical cell using the flow rate of the electrolyte. However, the control of the output voltage is not based on the current demands or power draw through the system. In addition, these systems require rather significant volumes of electrolyte to cause the desired cooling.
Therefore, the need exists for a system that controls the voltage output of an electrochemical cell based on the current power draw. In addition, the system should be able to use a relatively minimal volume of electrolytes, saving space and weight.